Title

Author

Date of Award

Spring 1-1-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry & Biochemistry

First Advisor

Jose L Jimenez

Second Advisor

Paul Ziemann

Third Advisor

Eleanor Browne

Abstract

We present results of the first intercomparison of real-time instruments for gas/particle partitioning of organic species. Four new instruments that directly measure gas/particle partitioning in near-real time were deployed at the Centreville, Alabama, Supersite of the Southern Oxidant Aerosol Study (SOAS) in the southeastern United States in the summer of 2013. Two were Filter Inlet for Gases and AEROsols High-Resolution Chemical Ionization Mass Spectrometers (FIGAERO-HRToF-CIMS) with acetate (A-CIMS) and iodide (I-CIMS) ionization sources, respectively, the third was a Thermal Desorption Aerosol GC-MS (TAG), and the fourth was a High-Resolution Thermal Desorption Proton-Transfer Reaction Mass Spectrometer (HR-TD-PTRMS). Signals from these instruments corresponding to elemental formulas of several organic acids are chosen for comparison of the measured gas/particle partitioning. Average partitioning of all common measured species shows a trend between TAG and A-CIMS with a slope of 1.86; between I-CIMS and A-CIMS with a slope of 1.68; and between PTRMS and A-CIMS and with a slope of 0.41. The comparison of time series show a substantial amount of scatter that is often averaged out in diurnal cycles to show similar diurnal trends, and absolute values that often agree within the error of the instruments. When the differences in partitioning observed among instruments are outside the estimated measurement errors, the causes may be due to measurement of different isomers resulting from differences in chemical sensitivities for different instruments, thermal decomposition during the heating cycles of the various instruments, or to other unidentified instrumental issues. There is some evidence for the presence of several isomers for several of the exact masses studied here from measurements using an ion mobility-CIMS at the field site. There is also evidence for the presence of several isomers and some thermal decomposition from the signal profiles of the heating cycles of the CIMS instruments. This study shows promise for a measurement that was not feasible until very recently, while it also points to the difficulty of this measurement and its interpretation in a complex ambient environment, and the need for further improvements in measurement methodologies. Further intercomparisons under controlled laboratory conditions are recommended.